9EE605A.13to141 Department of Technical Education Andhra Pradesh Name:V. Narsimha Reddy Designation:Lecturer in EEE Branch:D.E.C.E Institute:GMR. Polytechnic Gajwel Semester:VI Semester Subject:Electrical Utilization & Automation Code:EE605 A Topic:Electric Heating Duration:100 Minutes Sub topic:Methods of Temperature control Teaching Aids: PPT, Diagrams, Animation Revised By : K. Chandra Sekhar, L/EEE, GPT, HYD

9EE605A.13to142 Recap In the previous class you have learnt about Resistance heating Classification of resistance heating Applications of resistance heating

9EE605A.13to143 Objectives On completion of this topic,you would be able to know Different methods of temperature control of resistance heating

9EE605A.13to144 Temperature Control of Resistance Heating In resistance heating supply voltage and resistance of heating elements are independent parameters Current is a dependent parameter The temperature of resistance furnace is controlled by Supply voltage By varying the number of heating elements Switching ON and OFF the supply

9EE605A.13to145 Temperature Control Methods Temperature control of resistance heating Periodically switching on & off of the power supply By varying supply voltage By varying resistance By variable supply By Auto- T/F or Induction regulator By series impedance

9EE605A.13to146 Temperature Control Methods Temperature control of resistance heating Periodically switching on & off of the power supply By varying supply voltage By varying resistance By varying the number of heating elements By changing the arrangement & heating elements

9EE605A.13to147 By Variable Supply Voltage If the furnace has separate generating set for electric power supply, then variable voltage can be generated and supplied to the furnace depending upon the temperature Voltage can be variable This is usually employed for large capacity furnace

9EE605A.13to148 By Auto-transformer or Induction Regulator V 1 =Primary side supply voltage. V 2 =Secondary output voltage. I 1 =Primary current I 2 =Secondary current. Fig.1 F U R N A C E S u p p l y

9EE605A.13to149 By Auto-transformer or Induction Regulator Fig 1 shows an auto - transformer By changing the position of the tap the voltage supplied to heating element will change and accordingly the temperature S u p p l y Fig.1 F U R N A C E

9EE605A.13to – Phase Induction Regulator Fig 2 shows a single phase induction regulator By changing the position of rotor (primary) the output voltage v 2 will change The change controls the furnace temperature Fig 2

9EE605A.13to1411 By Series Impedance A variable impedance will be connected in series with the furnace A part of voltage drop across the impedance included and the remaining voltage appears across the furnace Due to inclusion of impedance of the coil,the power factor reduces A capacitor is connected across the supply to improve the powerfactor i.e., Dotted Lines Fig.3 S u p p l y

9EE605A.13to1412 By Varying The Number of Heating Elements In this method the number of heating elements are changed by operating the switches shown in fig 4 if the supply is reduced to all/few elements, the temperature also reduces and vice-versa. Fig.4

9EE605A.13to1413 By Varying The Number of Heating Elements The number of heating elements are changed by operating the switches shown in fig 4 Each element is provided with one switch in fig 4 (a) One switch controls three elements in fig 4(b) If the supply voltage is reduced to few / all elements the temperature reduces and vice – versa Non uniform heating taken place If uniform heating is required the even or odd number elements should be switched off in fig 4 (b)

9EE605A.13to1414 V V/2 V/4 V V Four parallel paths Two parallel paths one parallel path By Changing The Arrangement of Heating Elements Fig.5

9EE605A.13to1415 By Changing The Arrangement of Heating Elements Fig 5 (a) shows the arrangement of four heating elements for a single phase supply All the elements are in parallel, the heat produced will be equal to rating Fig 5 (a) V Four parallel paths

9EE605A.13to1416 By Changing The Arrangement of Heating Elements If four elements are arranged in two paths shown in fig 5 (b) The heat produced will be one – fourth Because the voltage across each element is v/2 Fig 5 (b) V V/2

9EE605A.13to1417 By Changing The Arrangement of Heating Elements If all four elements are arranged in series shown in fig 5 (c) The heat produced will be one – sixteenth Because the voltage in each element is v/4 Fig 5 (c) V/4 V

9EE605A.13to1418 By Changing The Arrangement of Heating Elements Fig 6 shows circuit configuration for 3 phase system When the same elements are changed from delta to star, the power consumption reduced to one - third Fig.6 Connected in star Connected in delta Three-Phase System

9EE605A.13to1419 Periodically / Intermittent On / Off Final temperature α Time interval the switch remains ON Total time interval of the ON/OFF cycle. The ON and OFF arrangement can be had by a thermostat switch. Which switches ON and OFF the supply at predetermined temperatures. Final temperature attained is proportional to ratio. The method is more efficient than series impedance method.

9EE605A.13to1420 Summary In this class we have discussed about Methods of temperature control of resistance heating

9EE605A.13to1421 Quiz 1. When four elements connected in parallel produce heat energy equal to the furnace. If the same four elements are arranged in two paths then the heat produced will be__________ that of the rated value. a.Half b.One-fourth c.One-sixteenth d.Equal

9EE605A.13to1422 Frequently Asked Questions 1)List the methods of controlling the temperature in resistance heating. 2) Explain the Auto T/F method of controlling the temperature. 3) Explain the method of controlling the temperature by varying the number of elements